Magnetic resonance imaging techniques provide the opportunity tovisualize internal organs at microscopic resolution in live animals and to conduct specialized studies on fixed blocks of pathologic specimens. The technology is sufficiently advanced utilizing proton imaging and hyperpolarized helium imaging that application of magnetic resonance microscopy can now be applied to toxicology studies. Through a combination of proton imaging and use of hyperpolarized helium imaging, distal airways in the live rat can be successfully imaged and functional measurements are possible. We have utilized a rat emphysema model to compare the differences between normal and emphysematous lungs utilizing magnetic resonance microscopy and resolutions approximately to the level of alveoli are possible. Studies utilizing paramegnetic contrast agents in fixed specimens have permitted delineation of the fine structure of organ vasculature. Current plans are to use this technology for assessment of teratogenic studies in rodents.